fix(install): command completion with single match

During a refactoring of the tests a bug was found in the install command
completion that would return nothing if there was a valid match, this
fixes that bug and also makes the tests actually test things.

lib/commands/install.js

@@ -77,38 +77,33 @@ class Install extends ArboristWorkspaceCmd {
       const partialName = partialWord.slice(lastSlashIdx + 1)
       const partialPath = partialWord.slice(0, lastSlashIdx) || '/'
 
-      const annotatePackageDirMatch = async sibling => {
-        const fullPath = join(partialPath, sibling)
+      const isDirMatch = async sibling => {
         if (sibling.slice(0, partialName.length) !== partialName) {
-          return null
-        } // not name match
+          return false
+        }
 
         try {
-          const contents = await readdir(fullPath)
-          return {
-            fullPath,
-            isPackage: contents.indexOf('package.json') !== -1,
-          }
+          const contents = await readdir(join(partialPath, sibling))
+          const result = (contents.indexOf('package.json') !== -1)
+          return result
         } catch (er) {
-          return { isPackage: false }
+          return false
         }
       }
 
       try {
         const siblings = await readdir(partialPath)
-        const matches = await Promise.all(
-          siblings.map(async sibling => {
-            return await annotatePackageDirMatch(sibling)
-          })
-        )
-        const match = matches.filter(el => !el || el.isPackage).pop()
-        if (match) {
-          // Success - only one match and it is a package dir
-          return [match.fullPath]
-        } else {
-          // no matches
-          return []
+        const matches = []
+        for (const sibling of siblings) {
+          if (await isDirMatch(sibling)) {
+            matches.push(sibling)
+          }
+        }
+        if (matches.length === 1) {
+          return [join(partialPath, matches[0])]
         }
+        // no matches
+        return []
       } catch (er) {
         return [] // invalid dir: no matching
       }